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In the Field

The ermine

    One day last week, as I was driving my youngest son to the bus stop, we

noticed something white rolling down our gravel driveway. At first it looked like a wrapper or a piece of paper blowing down the road. But there was

no wind.

    The object suddenly stopped moving, and we were able to determine the white object was an ermine wrestling with a meadow vole. The ermine had noticed us and let the vole go. As the vole dashed across the driveway, the ermine just couldn't resist and ran after the potential meal and caught it again. The ermine dashed back across the drive with the vole dangling from its mouth. It disappeared into the tall grass... gone from sight to eat it's tasty breakfast. The portion of the drama that we observed probably didn't last more than 20 seconds. But what an exciting event for a fourth grader to witness on the way to school...and for a dad on his way to the office, to write a column about wildlife. The experience prompted me to consult some books to learn more about the ermine.

    The ermine has a circumpolar distribution. It is found in the north

temperate and frigid sectors of Europe, Asia and North America. In the New World, it ranges from east to west in a broad belt from the Arctic Ocean and adjacent islands southward into the northern United States.

    At full adult size, the ermine's total body length from head to rump is seven to 12 inches. Males are generally twice as large as females. The tail length is about 35% of the total body length. Ermine have the typical weasel form: long body, short legs, long neck supporting a triangular head, slightly protruding round ears, bright black eyes, and long whiskers. Their short fur is white in the winter and the tip of the tail is black. In the summer, the back fur is chocolate brown while the underside fur extending to the upper lip is yellowish white. The one we observed had changed color well before the first snow of the season giving it a very striking appearance.

    Ermine are carnivores that hunt primarily at night. They are specialist predators on small, warm-blooded vertebrates. When mammalian prey is scarce, ermine eat birds, eggs, frogs, fish, and insects. In severe climates,

 ermine frequently hunt under snow and survive entirely on small rodents. Daily meals are essential to meet the ermine's exorbitant energy and heat production demands. Ermine cache leftover meals as a way of dealing with these demands.

    Ermine are polygamous and promiscuous. They mate in late spring to early summer. Females produce only one litter per year. Young are born in April or May after an average gestation period of 280 days, which includes an 89 month period of developmental delay. Longer days beginning in March trigger the resumption of fetal development. Litter size can be as high as 318 offspring and averages 49. Young are blind and helpless. They are covered with fine white hair, and a prominent dark mane of dense fur develops around the neck by the third week. The function of this is unknown.  The young grow quickly and are able to hunt with their mother by their eighth week. Although females do not reach adult size until a least six weeks after birth, they are able to mate when they are 6070 days old, often before they are weaned.

    Males do not breed or gain adult size until their second summer. Females in nature may survive for at least 2 breeding seasons, while males generally do not survive this long. Reproductive success is highly dependent on food availability.

    The ermine's lithe, agile body allows it to move swiftly both above ground and through underground burrows. Ermine can also run easily across snow. This ideal predator hunts in a zigzag pattern, progressing by a series of leaps of up to 20 inches each. Ermine investigate every hole and crevice, often stopping to survey their surroundings by raising their heads and standing upright on their hind legs. Once a potential prey is identified, the ermine approaches as closely as possible. With incredible speed it grasps the back of the victim's head and neck with sharp teeth, and wraps its body and feet around the victim. The victim dies from repeated bites to the base of the skull. Ermine have keen senses that help them locate prey. Hares and rodents are mainly followed by scent, insects by sound, and fish by sight.

    Ermine population densities fluctuate with prey abundance. Home ranges of males are usually twice the size of female home ranges which may explain the higher number of males that are trapped. These solitary mammals maintain exclusive boundaries that are patrolled and marked by scent.

    Adult males dominate females and young. Females tend to remain in their birth place throughout their lives. Males disperse and attain large territories that usually encompass or overlap females' territories. Male and female ermine only associate with one another during the breeding season.

    Ermine prefer riparian woodlands, marshes, shrubby fence rows, and open areas adjacent to forests or shrub borders. Although ermine are primarily terrestrial, they climb trees and swim well. Tree roots, hollow logs, stone walls, and rodent burrows are used as dens. Dens are usually around 12 inches below ground. Ermine line their nests with dry vegetation, and fur and feathers from prey. Side cavities of burrows are used as food caches and latrines.     Humans trap thousands of ermine each season, but the demand for pelts has declined. The white winter fur has long been used in trimming coats and making stoles. Ermine are excellent mousers, which makes them valuable to humans. Some farmers claim that ermine kill poultry, but this has rarely been documented.

    The average life span of an ermine is 12 years; the maximum is seven years. Potential enemies are usually larger carnivores including red fox, gray fox, martens, fishers, badgers, raptors (owls, primarily) and occasionally domestic cats.

 

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Phil Cooper

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